Abstract

Study objective: Our purpose was to study the
relationship between snoring and pregnancy-induced hypertension and
growth retardation of the fetus.

Design: Retrospective,
cross-sectional, consecutive case series.

Setting: The
Department of Gynecology and Obstetrics, University Hospital, Umeå,
Sweden.

Participants and measurements: On the day of
delivery, 502 women with singleton pregnancies completed a
questionnaire about snoring, witnessed sleep apneas, and daytime
fatigue. Data concerning medical complications were taken from the
women’s casebooks.

Results: During the last week
of pregnancy, 23% of the women reported snoring every night. Only 4%
reported snoring before becoming pregnant. Hypertension developed in
14% of snoring women, compared with 6% of nonsnorers (p < 0.01).
Preeclampsia occurred in 10% of snorers, compared with 4% of
nonsnorers (p < 0.05). An Apgar score ≤ 7 was more common in
infants born to habitual snorers. Growth retardation of the fetus,
defined as small for gestational age at birth, had occurred in 7.1% of
the infants of snoring mothers and 2.6% of the remaining infants
(p < 0.05). Habitual snoring was independently predictive of
hypertension (odds ratio [OR], 2.03; p < 0.05) and growth
retardation (OR, 3.45; p < 0.01) in a logistic regression analysis
controlling for weight, age, and
smoking.

Conclusions: Snoring is common in
pregnancy and is a sign of pregnancy-induced hypertension. Snoring
indicates a risk of growth retardation of the fetus.

Preeclampsia,
defined as pregnancy-induced hypertension and proteinuria, frequently
combined with edema, is asymptomatic in some women but may induce
severe symptoms in others.1 Hypertensive disorders during
pregnancy are a leading cause of maternal death in the United States
and Great Britain1–2 and are important causes of neonatal
morbidity and mortality.3–4 The cause of these diseases
is, however, still unknown.

Gislason et al5 found that snoring was strongly related to
hypertension in middle-aged women. Snoring is a sign of increased upper
airway resistance and obstructive sleep apnea,5–7 which
is associated with arterial hypertension and coronary artery
disease.8–10 Muscle sympathetic nerve activity and
nocturnal norepinephrine levels are elevated in these patients and are
considered to be a possible cause of sleep apnea-induced
hypertension.11–12

Snoring and sleep apnea are often caused by factors that narrow the
upper airway. Both nasal congestion and pharyngeal edema are such
constricting factors occurring during pregnancy.13–
However, only a few case reports including sleep apnea and
complications during pregnancy are available.14–17
One of these reports relates to a case of intrauterine growth
retardation,15 and one describes a woman with
preeclampsia.17Loube et al18 reported that
snoring frequency increases during pregnancy, but no one has
investigated whether snoring is associated with hypertensive disorders
of pregnancy.

In the present study, we investigated the association of self-reported
snoring with complications of pregnancy and fetal outcome.

Materials and Methods

The study was performed at the Department of Obstetrics and
Gynecology at Umeå University Hospital. A questionnaire was
administered by four midwives to 518 consecutive women on the day of
delivery. Women who underwent cesarean section and those who gave birth
to a dead baby or twins were not included. All but 16 women completed
the questionnaires. Complete answers were thus obtained from 502 women
with singleton pregnancies. The women had a mean weight of
74.5 ± 12.0 kg, and they were 28.9 ± 5.0 years old at delivery.
All but 10 women were white and were born either in Sweden or
Finland.

Questionnaire

When a woman answered the questionnaire she was, as a rule,
accompanied by her partner. The questionnaire was administered when she
entered the hospital on the day of delivery. She was asked to rate her
snoring frequency before pregnancy and during the last week before
delivery according to a five-point scale corresponding to never,
seldom, sometimes, often, or always. She was also asked about the time
during the pregnancy when the snoring began. Habitual snoring was
considered if snoring frequency was rated as often or always at the day
of delivery.

Excessive daytime sleepiness was defined as an answer of “Yes, a
lot” to the question, “Did you experience excessive daytime
sleepiness during the pregnancy?” The other possible answers were,“
No, it was as usual” or “No, I became more alert during the
pregnancy.”

The questions also related to smoking habits, medication, and
concomitant disease. Her partner was asked if he had noted apneas
during sleep. They were both asked to cooperate on questions of snoring
and witnessed sleep apneas.

BP measurements

The BP measurements were recorded in each woman’s medical
chart. All of the studied women had attended the prenatal clinic where
investigations, including BP measurements in the supine position, were
made at gestational weeks 8–10, 12, 25, 28, 31, 33, 35, 37, 39, and
41. Follow-up BP measurements were recorded more frequently when an
increased BP was observed.

Complications

The women’s edema was rated from 0 to 3, and their body weight
was recorded before delivery. Data concerning medical complications
were taken from the women’s casebooks.

Recordings were obtained from the infants’ birth weight,
length, sex, head size, and Apgar score at 1 and 5 min after birth. The
Apgar score was based on heart rate, respiratory effort, muscle tone,
reflex irritability, and skin color.19 Each variable was
rated from 0 to 2, where 2 was normal. The maximum Apgar score was 10.

Definitions

Pregnancy-induced hypertension was defined as repeated BP
recordings > 140/90 mm Hg appearing during the pregnancy. Four women
had hypertension prior to the pregnancy and were, thus, not regarded to
suffer from pregnancy-induced hypertension. Preeclampsia was defined as
pregnancy-induced hypertension with proteinuria ≥ 0.3 g/24 h. Growth
retardation of the fetus was considered when the infant was small for
gestational age according to a birth weight below 2 SDs on the Swedish
standard chart.20

Statistical Analysis

The data are presented as mean ± SD for continuous variables
and as rates for nominal values. Differences between two means were
assessed using Student’s t test for independent samples.
Differences between proportions were analyzed using theχ
2 test. Fisher’s two-tailed Exact Test was
used when appropriate. Multiple logistic regression was used to analyze
the relationship between snoring and complications of pregnancy. The
null hypothesis was rejected at the 5% level (p < 0.05).

Results

Snoring frequency increased during pregnancy (p < 0.001). Of
the total sample, 7% of the pregnant women stated that they started to
snore or markedly increased their snoring frequency during the first
trimester, 6% during the second trimester, and 24% during the third
trimester. Habitual snoring rated as every night or almost every night
was reported by 23% of the pregnant women during the last week before
delivery. Occasional snoring was reported by another 25%. Only 4% of
the women reported that they had snored habitually, and 22% snored
occasionally before becoming pregnant.

Witnessed sleep apneas were observed in 11% of habitual snorers, as
compared with 2% of the nonhabitual snorers (p < 0.001). Women who
snored habitually had a mean weight of 64.1 ± 14.3 kg before
becoming pregnant, which was more than the remainder of the women, who
weighed 59.5 ± 10.3 kg (p = 0.002). The habitually snoring women
also had a more pronounced weight increase during pregnancy
(p < 0.05) and were slightly older than the rest (p < 0.05; Table 1
).

Preeclampsia and Pregnancy-Induced Hypertension

Fourteen percent of the women who snored habitually had
pregnancy-induced hypertension as compared with 6% of the nonsnorers
(p < 0.01). Ten percent of the women who snored met the definition
of preeclampsia with hypertension and proteinuria as compared with 4%
of the nonsnorers (p < 0.05). All the patients with preeclampsia who
snored habitually during the last week of pregnancy had started to
snore during the pregnancy and before any sign of preeclampsia was
present.

Witnessed sleep apneas tended to be more frequent in women with
preeclampsia (p = 0.069) and pregnancy-induced hypertension
(p = 0.055). They were reported in 12% of women with preeclampsia
and 10% of women with hypertension.

Habitual snoring was a risk factor, independent of weight, age and
smoking habits, for pregnancy-induced hypertension (odds ratio [OR],
2.03; p < 0.05) and also tended, but not significantly, to be
an independent risk factor for preeclampsia (OR, 2.18; p = 0.07)
according to the multiple logistic regression analysis (Table 2
).

Excessive Daytime Sleepiness

Excessive daytime sleepiness was subjectively reported in as many
as 65% of the women. It started during the first trimester in 25% of
the women, during the second trimester in 18%, and during the third
trimester in 22%. The prevalence of excessive daytime sleepiness was
similar among women who snored habitually and among those who did not
(Table 1). In general, daytime sleepiness started earlier in pregnancy
than did snoring.

Edema

Edema was overrepresented among women who snored habitually. Edema
of the face, hands, legs, or feet occurred in 52% of the habitual
snorers compared with 30% of the remainder (p < 0.001). Facial
edema was observed in 27% of the habitual snorers, compared with 10%
of the remaining women (p < 0.001).

Infant Outcome

Eight of the 113 habitual snorers (7.1%) delivered an infant with
growth retardation at birth (small for gestational age), compared with
10 of 379 of the nonhabitual snorers (2.6%; p < 0.05). Snoring
remained as a significant predictor of growth retardation (OR, 3.45;
p < 0.01) in the multiple logistic regression after adjustment for
weight, age, and smoking habits (Tables 3, 4
). Smoking was also found to be an independent predictor of growth
retardation (OR, 3.94; p < 0.01).

An Apgar score ≤ 7 was more common in infants born to habitual
snorers compared with infants born to occasional snorers and
nonsnorers, 1 and 5 min after delivery (Table 3).

Habitual snoring did not influence the ratio of birth weight to
placenta weight. Witnessed sleep apneas of the mother did not relate to
infant outcome.

Discussion

In the present study, habitual snoring during pregnancy was
related to hypertension, preeclampsia, edema, and increased body
weight. Habitual snoring in the mother was also associated with growth
retardation of the fetus and a low Apgar score for the infant. Habitual
snoring was independently predictive of hypertension and growth
retardation, even when weight, age, and smoking were controlled for.

Snoring may be regarded as a common feature of pregnancy, as 23% of
the women in this study snored habitually and 25% snored occasionally,
whereas only 4% had snored habitually prior to pregnancy. Loube et
al18 found that habitual snoring occurred in 14% of
pregnant women (n = 350). The women answered the questionnaire on the
day of delivery in the present study, and not during the second or
third trimester as was the case in the study by Loube et
al.18 They did not find any effect on the infants, while
we found an increased frequency of infants born small for gestational
age.

The increased frequency of infants born small for gestational age and
low Apgar scores in the infants of snoring mothers is a novel finding.
It indicates that the consequences of increased upper airway resistance
during sleep may affect the fetus and supports the previously suggested
relationship between sleep apnea and intrauterine growth
retardation.15

The association between snoring and pregnancy-induced hypertension and
preeclampsia is also a novel finding that has not previously been
studied. It is not possible to draw any firm conclusions about the
cause and effect because of the present study design. However, all of
the subjects who snored habitually and had preeclampsia started to
snore before any sign of hypertension or proteinuria was present, and
habitual snoring was related to witnessed sleep apneas. This indicates
that nocturnal upper airway obstruction may contribute to the
development of pregnancy-induced hypertension and preeclampsia. It is
possible that pregnant women are especially vulnerable to increases in
upper airway resistance, as breathing may also be restricted by an
increase in the abdominal pressure affecting the diaphragm. Respiratory
sleep studies, including the treatment of sleep apnea in women with
preeclampsia, are desirable and may answer the question of whether
there is an etiologic link between increased upper airway resistance
and preeclampsia.

Apart from snoring, excessive daytime sleepiness is the most common
symptom of obstructive sleep apnea.21 A majority of the
present women reported that they had experienced excessive daytime
sleepiness during the pregnancy. It was not, however, overrepresented
among those who snored habitually, and sleepiness often began earlier
in pregnancy than snoring. Similar to our findings, Loube et
al18 could not find any relationship between daytime
sleepiness and snoring in pregnant women using the Epworth sleepiness
scale. On the contrary, they reported that the Epworth sleepiness score
was the same for pregnant and nonpregnant women. Whether or not
excessive daytime sleepiness is induced by pregnancy is still unclear.
However, it is likely that complaints of daytime fatigue and sleepiness
during pregnancy are due to factors other than disturbed sleep due to
snoring.

Snoring is the audible sign of an increase in upper airway resistance.
In this study, the snoring frequency depended on the extent to which
the bedroom partner perceived it. There is no international consensus
on the objective definition of snoring, although objective recordings
using microphones correlate well with subjective snoring in young
adults.22 Subjective reports are, however, the most
commonly used instrument for measuring snoring, partly because of the
technical problems involved with microphone recordings and partly
because the subjective reports give an average of the subject’s degree
of snoring, whereas the result of the recording of a single night may
be misleading.

A limitation with cross-sectional surveys is that it is not possible to
draw any conclusions regarding the cause and the effect. A confounding
effect of an uncontrolled factor could have been responsible for the
present results even though snoring appears to be a risk factor.
Possible confounding factors not controlled for in the present study
were, for example, the body mass index, the parity, and the social
status. Another limitation is that snoring was based on subjective
reports. However, this is a problem also in other epidemiologic studies
of snoring.

Women who reported habitual snoring were heavier before pregnancy and
gained more weight during pregnancy. Edema was more common in habitual
snorers. It may be speculated that pharyngeal swelling could narrow the
upper airway to a critical point at which snoring would occur. Weight
gain and pharyngeal edema are therefore possible causes of
pregnancy-induced snoring. Nasal congestion due to hormonal changes
may, however, also have contributed to snoring, since 7% reported that
they started to snore during the first trimester.

Snoring is common in pregnancy and is a sign of pregnancy-induced
hypertension. Snoring indicates a risk of growth retardation of the
fetus.

Abbreviation: OR = odds ratio

The study was supported by grants from the Swedish Heart and Lung
Foundation and the Swedish Association for Heart and Lung Patients.

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